GIFT  OF 


i'wA 

It: 


I  OUR     CLIMATE 

!#?£ 

Useful  Information  regarding  the  Climate  between 

the  Rocky  Mountains  and  the    Atlantic 

Coast,  with  special  reference  to 


MARYLAND 

-AND- 

DELAWARE 

Prepared  by 

JAMES  H.  SPENCER,  Meteorologist 
BALTIMORE,  MD. 


Issued  by  the 

»  MARYLAND  STATE  WEATHER  SERVICE 

In  cooperation  with  the 

UNITED  STATES  WEATHER  BUREAU 
CHARLES  F.  MARVIN.  Chief 


Board  of  Government,  Maryland  State  Weather  Service :  Director,  Prof.  Edward  B.  Mathews, 
Johns  Hopkins  University,  Baltimore,  Md.  ;  Secretary  and  Treasurer,  Prof.  W.  T.  L.  Taliaferro, 
University  of  Maryland,  College  Park,  Md.  ;  Meteorologist,  James  H.  Spencer,  U.  S.  Weather 
Bureau,  Baltimore,  Md. 


TV  /[  ARYLAND  AND  DELAWARE  have  an  excellent  corps  of  Cooperative 
+  *  *  Observers,  many  of  whom  have  been  taking  daily  weather  observations 
for  the  United  States  Weather  Bureau  and  the  Maryland  State  Weather 
Service  for  more  than  a  quarter  of  a  century.  Except  for  the  faithful  work 
that  these  Cooperative  Observers  are  doing,  the  publication  of  this  Booklet 
would,  of  course,  be  impossible.  In  its  preparation  the  records  of  about  65 

stations  in  Maryland  and  Delaware 
have  been  used.  The  equipment 
of  a  Cooperative  Observer  consists 
of  a  maximum  and  a  minimum  ther- 
mometer, a  thermometer  shelter,  and 
a  rain  gage. 

An  intelligent  idea  of  one's 
climate  can  best  be  obtained,  per- 
haps, by  comparing  climatic  data  for 
the  various  sections  of  the  country, 
and  this  is  the  reason  why  data  are 
included  in  this  Booklet  for  all  sections 
of  the  United  Slates  east  of  the  Rocky 
Mountains.  Most  of  the  information 
that  relates  to  other  States  was  fur- 
nished by  Weather  Bureau  officials 
especially  for  this  Booklet,  but  some 
COOPERATIVE  OBSERVER'S  EQUIPMENT  of  lhe  averages  tnat  change  only 

slightly  from  year  to  year  were  taken  from  Bulletin  Q,  published  by  the 
United  States  Weather  Bureau 

Our  thanks  for  valuable  assistance  in  the  preparation  of  this  Booklet  are  due 
to  Mr.  Joseph  Bily,  Jr.,  Meteorologist,  and  to  other  members  of  the  Weather 
Bureau  force,  at  Baltimore,  Md. ;  also  to  Prof.  Charles  F.  Marvin,  Prof.  Edward 
B.  Mathews,  and  Prof.  W.  T.  L.  Taliaferro  for  many  helpful  suggestions. 

JAMES  H.  SPENCER, 

Meteorologist. 


Write  to  Local  Office,  V.  S.  Weather  Bureau,  Baltimore,  Md  ,  for  Bulletins  94  and  9o.  These 
Bulletins,  published  by  the  Weather  Bureau,  contain  complete  data  for  all  cooperative  weatherstations 
in  Maryland  and  Delaware.  Teachers  may  also  obtain  free  of  charge  from  the  same  source,  :•!  beautiful 
Maryland  State  Weather  Service  Climatic  Maps,  printed  in  colors. 

3 


on  i  , 


OUR  CLIMATE 


OUTSTANDING  FEATURES 

We  present  in  this  Booklet  some  evidence  that  the  Climate  of  Maryland  and 
Delaware,  when  considered  "all-the-year-round,"  is  one  of  the  best  in  the 
United  States. 

Winters  are  mild,  although  characterized  by  weather  that  does  not  lack 
invigorating  qualities.  "Zero"  weather  has  been  recorded  at  Baltimore  only  1  3 
times  in  50  years,  and  the  lowest  recorded  during  this  50-year  period  was  7° 
below  zero.  During  a  20-year  period  "zero"  weather  was  recorded  only  5  times 
at  Cambridge,  9  times  at  Easton,  12  times  at  Princess  Anne,  15  times  at 
Cheltenham,  32  times  at  Laurel,  and  36  times  at  Frederick. 

Summers  are  warm,  as  in  other  good  agricultural  sections  of  the  United  States. 
They  are,  however,  usually  tempered  by  cool  spells  that  originate  in  more  northern 
latitudes,  frequently  in  the  Hudson  Bay  Region  of  Canada.  Spring  and  Autumn 
are  both  delightful  seasons. 

The  geographic  position  of  these  States  with  reference  to  the  usual  storm 
paths  is  decidedly  favorable  for  a  uniform  and  abundant  supply  of  moisture  for  all 
purposes.  The  annual  precipitation  averages  41.61  inches  in  Maryland  and 
43.25  inches  in  Delaware. 

The  average  annual  snowfall  is  moderate,  amounting  to  2  7  inches,  unmelted, 
in  Maryland  and  Delaware.  Snow  does  not  remain  long  on  the  ground,  as  a  rule. 

"Gloomy"  weather  is  conspicuous  by  its  absence.  The  sun  shines  at 
Baltimore  during  some  portion  of  the  day  on  about  32  1  days  in  the  year,  on  the 
average.  "Winter  Sunshine"  is  nearly  double  the  amount  which  occurs  over  a 
large  portion  of  the  Lower  Lake  Region.  Yet  days  with  1  00  per  cent,  of  sun- 
shine are  rather  rare  at  any  season  of  the  year,  and  a  typical  day  is  one  on  which 
the  sky  is  partly  covered  with  clouds. 

The  "growing  season,"  or  frost-free  period,  is  remarkably  long  for  the 
latitude  in  which  Maryland  and  Delaware  are  located,  averaging  about  185  days. 

There  is  little  difference  in  the  climate  along  the  two  shores  of  Chesapeake 
Bay,  either  as  to  temperature  or  precipitation. 

Severe  storms  are  infrequent,  prolonged  droughts  are  of  rare  occurrence,  and 
there  is  almost  a  total  freedom  from  tornadoes. 

4 


MARYLAND  AND  DELAWARE 


38.. 


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lyn 

15  3S    .fc 


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' 


OUR  CLIMATE 


THE  LATEST  FACTS  ABOUT  THE  RAINFALL  OF  MARYLAND 

AND  DELAWARE. 

The  records  of  69  cooperative  stations  in  Maryland  and  Delaware  show 
that  the  average  annual  precipitation  for  Maryland  is  41.61  inches ;  and  for 
Delaware,  43.25  inches. 

The  annual  precipitation  for  the  various  sections  of  Maryland  and  Delaware 
is  remarkably  uniform  and  well-distributed  through  the  year,  and,  except  in  St. 
Mary's  County  and  the  Cumberland  Valley,  falls  between  40  and  47  inches. 
The  maximum  monthly  amounts  occur  in  August  and  the  minimum  monthly 
amounts  occur  in  November. 

The  average  monthly  amounts,  in  inches,  for  the  two  States  as  a  whole,  are 
shown  in  the  following  table : 

MONTH  MD.        DEL.        MONTH  MD.         DEL. 


I  any.  .  . 

.      3.28 

3.26 

July 

4.30 

453 

Feby... 

.  .  3.02 

3.32 

AUK 

.     4.43 

456 

March.... 

....3.61 

3.80 

Sept 

.3.18 

378 

April  

....3.37 

3.43 

Oct  

,...2.96 

1  19 

Mav  .. 

..3.55 

3.67 

Nov... 

..2.47 

2.76 

June 4.14    3.76       Dec 3.30    3.69 

The  ten  stations  having  the  longest  records  for  the  entire  Maryland-Delaware 
section,  together  with  the  average  annual  amounts,  in  inches,  are  given  in  the 
following  table : 

Annapolis 46.45  Fallston 46.90 

Baltimore 43.18  Frederick 40.47 

College  Park 41.55  Woodstock  College... 41 .98 

Cumberland 34.87  Washington,  D.  C 43.50 

Emmitsburg 44.24  Milford,  Del 44.67 

The  average  length  of  these  9  stations  in  Maryland  and  the  District  of 
Columbia  is  only  slightly  less  than  50  years;  and  for  Milford,  Del.,  it  is  38  years. 
Meteorologists  and  Agriculturists  agree  that  in  sections  of  the  World  without 
irrigation  the  annual  precipitation  should  usually  fall  between  25  and  50  inches 
for  the  best  results;  and  that  precipitation  must  be  well  distributed  through  the 
crop  season,  as  in  Maryland.  For  further  precipitation  data,  see  pages  5,11,  and  12. 

6 


MARYLAND  AND  DELAWARE 


OUR  CLIMATE 


THE  LATEST  FACTS  ABOUT  THE  TEMPERATURE  OF 
MARYLAND  AND  DELAWARE. 

Except  in  the  mountainous  regions  of  Maryland,  the  general  physical  features 
of  Maryland  and  Delaware  are  not  favorable  for  great  local  climatic  differences, 
but  rather  for  uniformity  in  the  prevailing  weather  conditions.  Hence,  it  is  not 
surprising  that  the  differences  in  the  average  monthly  temperatures  for  the  various 
stations  are  small  and  fairly  constant. 

East  of  the  mountains,  the  range  in  annual  temperature  is  from  52°  in  the 
extreme  northern  portion  to  57°  in  the  extreme  southern.  The  average  annual 
temperature  for  Maryland  is  53.4°  ;  and  for  Delaware,  54.9°. 

The  average  monthly  temperatures,  in  degrees  Fahrenheit,  for  the  two  States, 
are  shown  in  the  following  table : 

MONTH  MD.        DEL.        MONTH  MD.        DEL. 


Jany  
Feby 

32.4 
.     .32.1 

34.2 
33.8 

July  
Aug 

..74.9 
.  73.1 

76.6 
748 

March  .  . 
April.... 

41.9 
52.1 

42.7 
52.7 

Sept  
Oct  

.66.9 
.56.2 

68.4 
578 

Mav... 

...62.7 

63.6 

Nov... 

..44.2 

46.0 

June 70.2     71.6       Dec 34.3     36.5 

The  ten  stations  having  the  longest  record  for  the  entire  Maryland -Delaware 
Section,  together  with  the  average  annual  temperature,  in  degrees  Fahrenheit,  are 
shown  in  the  following  table : 

Annapolis 55.7  Fallston 52.3 

Baltimore 55.3  Frederick 53.8 

College  Park 54.1  Woodstock  College 53.2 

Cumberland 52.4  Washington,  D.  C 54.9 

Emmitsburg 52.5  Milford,  Del 55.9 

For  further  temperature  data,  see  pages  7,  13,  14,  15,  and  1  6. 


MARYLAND  AND  DELAWARE 


II 

I! 


«  a 

II 


H  "3 
0-e 


OUR  CLIMATE 


This   Diagram  shows   HOW    THE    WIND 


YEAR 
I57o 


BLEW  for  a  11-year  period  at  Baltimore,  as 
recorded  by  a  vane  exposed  27.5  feet  above 
the  roof  of  the  Custom  House.  Note  that 
for  the  Year  the  most  frequent  direction 
was  Southwest  (18  per  cent.),  and  the  least 
frequent  direction  was  East  (6  per  cent.). 
In  WINTKK  the  most  frequent  direction 
was  Southwest  (20  per  cent.)  and  the  least 
frequent  direction  was  East  (5  per  cent,). 
In  SUMMER  the  most  frequent  direction 
was  South  (21  per  cent.),  and  the  least  fre- 
quent direction  was  West  (5  per  cent.).  In 
Summer,  however,  the  wind  blew  South- 
west and  South  combined  39  percent,  of  the 
time.  In  Spring  and  Autumn  there  is  a 
marked  similarity  in  the  percentages  for 
the  respective  directions.  This  Diagram  is 
computed  from  hourly  directions. 


WINTER 
16% 


SPRING 


11% 


18% 


10 


MARYLAND  AND  DELAWARE 


3V 

(•3°r 


GULF  OF  MEXICO 

#  Less  than  1   inch. 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  AVERAGE 
ANNUAL  PRECIPITATION  (in  inches),  and  the  numbers  in  parentheses 
show  the  AVERAGE  ANNUAL  UNMELTED  SNOWFALL  (in  indies). 
For  instance,  at  Baltimore  the  Average  Annual  Precipitation  is  43  inches,  and  vhe 
Average  Annual  Unmelted  Snowfall  is  24  inches.  By  "Precipitation,"  we  mean 
the  amount  of  rain  and  melted  snow. 


In  MARYLAND  and  DELAWARE  the  Average  Annual  Precipitation 
(in  inches)  and  the  Average  Annual  Unmelted  Snowfall  (in  inches)  for  a  few 
selected  cooperative  weather  stations  are  as  follows:  Annapolis,  46.4  and  23. 
College  Park,  41.6  and  19.  Easton,  40.7  and  16.  Fallston,  46.9  and  26. 
Frederick,  40.5  and  27.  Oakland,  45.7  and  69.  Princess  Anne,  41.8 
and  1 4.  Solomons,  36.5  and  1  8.  Millsboro,  Del.,  44.4  and  1  7.  Wilmington, 
Del,  44.4  and  23. 

11 


\ 


OUR  CLIMATE 


100 
(136T 

79                       10Q  \126\    '<!$ 

NOKTHPtfiTTf    100  ...iiSL  ,  CV/OqeA^ 

(i53)  fmr^)/^7 

104  (  Ti87) 
74 


119    . 

RICHMOND^ 

(207) 
130 
Jffi   ^>  V 

SHCtUfr     KNOXVILIE  \£>J.<3l         .X  .V» 

208)        (*207)  >  ^ 

119  r  '     0° 


[2201 
118 

MONT60M£Ry 

(246) 


207) 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  ANNUAL 
NUMBER  OF  DAYS  WITH  .01  OF  AN  INCH  OR  MORE  OF 
PRECIPITATION,  and  the  numbers  in  parentheses  show  the  NUMBER  OF 
PAYS  THAT  INTERVENE  BETWEEN  THE  AVERAGE.  DATE 
.OF  LATEST  KILLING  FROST  IN  SPRING  AND  THE  AVERAGE 
DATE  OF  EARLIEST  KILLING  FROST  IN  AUTUMN.  This  period 
is  commonly  known  as  the  "Growing  Season." 

At  Baltimore,  for  instance,  1  29  days  in  the  year  on  the  average  give  .01  of 
an  inch  or  more  of  Precipitation,  and  the  Average  Lenglh  of  the  Growing  Season 
is  2  1  5  days. 

The  Average  Length  of  the  Growing  Season  in  Maryland  as  a  whole  is  1  85 
days,  though  it  varies  for  the  various  divisions  of  the  State.  See  Map,  page  9. 

12 


MARYLAND  AND  DELAWARE 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  ANNUAL 
MEAN  TEMPERATURE  (in  degrees  Fahrenheit),  and  the  numbers  in 
parentheses  show  the  AVERAGE  ANNUAL  NUMBER  OF  DAYS  WITH 
MAXIMUM  TEMPERATURE  90°  OR  ABOVE.  For  instance,  at 
Baltimore  the  Annual  Mean  Temperature  is  55°,  and  there  is  an  average  of  20 
days  in  the  year  when  the  Maximum  Temperature  is  90°  or  above. 


In  MARYLAND  and  DELAWARE  the  Annual  Mean  Temperature 
and  the  Average  Annual  Number  of  Days  with  Maximum  Temperature  90°  or 
above  for  a  few  selected  cooperative  weather  stations  are  as  follows :  Annapolis, 
56°  and  22.  College  Park,  54°  and  31.  Easton,  55°  and  14.  Fallston, 
52°  and  10.  Frederick,  54°  and  31.  Oakland,  47°  and  2.  Princess 
Anne,  56°  and  10.  Solomons,  57"  and  23.  Millsboro,  Del.,  55°  and  26. 
Wilmington,  Del,  54V  and  21. 

13 


OUR  CLIMATE 


MAP    SHOWING    THE    HIGHEST   AND    LOWEST    TEMPER- 
ATURES OF  RECORD,  IN  DEGREES  FAHRENHEIT, 
FOR  THE  VARIOUS  CITIES. 


At  Cincinnati,  Ohio,  for  instance,  the  highest  temperature  ever  recorded  is 
1  05°  and  the  lowest  is  1  7°  below  zero,  as  shown  on  the  map.  At  Baltimore  1  05° 
occurred  on  August  5,  1918,  and  7°  below  zero  occurred  on  February  10, 
1  899  ;  these  are  the  highest  and  lowest  temperatures  at  Baltimore  in  a  5  2 -year 
period,  beginning  in  1871.  

In  MARYLAND  and  DELAWARE  the  highest  and  lowest  temperatures 
ever  recorded  at  a  few  selected  cooperative  stations  are  as  follows :  Annapolis, 
106  and— 6.  College  Park,  106  and  —26°.  Easton,  101  and  —15°. 
Fallston,  103  and— 14.  Frederick,  104°  and  — 2  I  .  Oakland,  101°  and 
—40°.  Princess  Anne,  99  and  —  1  0  .  Solomons,  1  04  and  — 5  .  Millsboro, 
Del.,  1  06°  and  — 17°.  Wilmington,  Del.,  1  0  7°  and  —  1  2  .  Highest  temperatures 
were  recorded  in  most  cases  on  August  6  or  7,  1918.  Lowest  temperatures  were 
recorded  in  most  cases  in  February,  1899,  or  January,  1912. 

14 


MARYLAND  AND  DELAWARE 


67 


82. 

5X1/V  AHTON/0 

(54) 


(55) 
GULF  OF  MEXICO 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  AVERAGE 
SUMMER  TEMPERATURE,  and  the  numbers  in  parentheses  show  the 
AVERAGE  WINTER  TEMPERATURE.  For  instance,  at  Baltimore  the 
Average  Summer  Temperature  is  76°,  and  the  Average  Winter  Temperature  is  35°. 


IN  DEGREES  FAHRENHEIT. 


In  MARYLAND  and  DELAWARE  the  Average  Summer  Temperature 
and  the  Average  Winter  Temperature  for  a  few  selected  cooperative  weather 
stations  are  as  follows:  Annapolis,  76  and  35.  College  Park,  73  and  34. 
Easton,  74  and  35  .  Fallston,  72  and  32 ".  Frederick,  74  and  33  . 
Oakland,  65  and  28 ".  Princess  Anne,  74  and  38  .  Solomons,  76  and 
36  .  Millsboro,  Del.,  74  and  35  .  Wilmington,  Del.,  74  and  33°. 

15 


OUR  CLIMATE 


GULF  OF  MEXICO 

#Less  than  1, 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  AVERAGE 
ANNUAL  NUMBER  OF  DAYS  WITH  MINIMUM  TEMPERATURE 
BELOW  FREEZING,  and  the  numbers  in  parentheses  show  the  AVERAGE 
ANNUAL  NUMBER  OF  DAYS  WITH  MINIMUM  TEMPERATURE 
BELOW  ZERO.  For  instance,  at  Baltimore  the  Average  Annual  Number  of 
Days  with  Minimum  Temperature  below  Freezing  is  76,  and  the  Average 
Annual  Number  of  Days  with  Minimum  Temperature  below  Zero  is  less  than  1 . 


In  MARYLAND  and  DELAWARE  the  Average  Annual  Number 
of  Days  with  Minimum  Temperature  below  Freezing  and  the  Average  Annual 
Number  of  Days  with  Minimum  Temperature  below  Zero  for  a  few  selected  co- 
operative weather  stations  are  as  follows :  Annapolis,  85  and  less  than  1 . 
College  Park,  120  and  2.  Easton,  92  and  less  than  1.  Fallston,  110 
and  1.  Frederick,  105  and  2.  Oakland,  163  and  10.  Princess  Anne, 
105  and  less  than  1.  Solomons,  74  and  less  than  1.  Millsboro,  Del., 
I  03  and  1 .  Wilmington,  Del.,  82  and  1 . 

16 


MARYLAND  AND  DELAWARE 


Apr.  1 
S   Oct8°24 


Goo/of  c/ry 

Oct.  19 


Aur  9  \  Apr.  1 
.*&sc/A  Oct.  1 
Oct.  24^) 


4BJ* 


Nov.  5 


ST.iOU/S 

Apr.  4\ 
Oct.  29 


Apr.  5  \\j 
uct.  <;t>        w/vMo/wl  \/ 

Oct.  29  lU 


Aprvl^^ 

Mar.  1 

Mar.  J6    ^NoTlS 
Nov^l5! 


ipr.  2    Apr.  3 

r-v/)wi////A   KNoyviue 

Oct.  27  Oct.  27 

Man  31 
Nov^e 
Mar.  10 

MONTGOMERY 

Nov-  n  Feb.  16 


'fer^?1 


Feb. 

NTON/0 

Nov.  28 


GULF  OF  MEXICO 


In  this  Map  the  upper  dates  for  the  various  cities  indicate  the  AVERAGE 
DATE  OF  LATEST  KILLING  FROST  IN  SPRING,  and  the  lower 
dates  indicate  the  AVERAGE  DATE  OF  EARLIEST  KILLING  FROST 
IN  AUTUMN.  For  instance,  at  Baltimore  the  Average  Date  of  Latest  Killing 
Frost  in  Spring  is  April  4,  and  the  Average  Date  of  Earliest  Killing  Frost  in 
Autumn  is  November  5. 

In  practically  all  sections  of  the  United  States  the  Average  Date  of  Latest 
Killing  Frost  in  Spring  is  a  few  days  earlier  in  cities  than  in  the  surrounding 
country,  and  the  Average  Date  of  Earliest  Killing  Frost  in  Autumn  is  a  few  days 
later  in  the  cities  than  in  the  surrounding  country.  That  is,  the  Growing  Season 
is  slightly  longer  in  cities  than  in  rural  districts.  See  the  Maryland-Delaware  Map, 
page  9,  for  additional  frost  data. 


17 


OUR  CLIMATE 


In  this  Map  the  upper  numbers  for  the  various  cities  show  the  AVERAGE 
SUMMER  RELATIVE  HUMIDITY,  and  the  numbers  in  parentheses  show 
the  AVERAGE  SUMMER  TEMPERATURE.  For  instance,  at  Baltimore 
the  Relative  Humidity  in  Summer  averages  70^,  and  the  Temperature  in  Summer 
averages  76°. 

The  Relative  Humidity  values  given  on  this  map  are  the  mean  of  observations 
taken  at  8  A.  M.  and  8  P.  M.,  75th  Meridian  Time,  and  are  expressed  as  a 
percentage.  The  Average  Summer  Temperatures,  which  are  the  numbers  in 
parentheses,  are  in  degrees  Fahrenheit.  The  most  uncomfortable  periods  of 
Summer  occur,  as  a  rule,  when  both  the  Temperature  and  the  Relative  Humidity 
are  high. 


18 


MARYLAND  AND  DELAWARE 


"WEATHER  SIGNS"  IN  MARYLAND  AND  DELAWARE. 

SOME  FACTS  ABOUT  THE  WEATHER  OF  VALUE  TO  MOTOR-BOATMEN, 
AUTOMOBILISTS,  FARMERS,  AVIATORS,  AND  OTHERS. 

A  typical  day  in  Maryland  and  Delaware  is  one  on  which  partly  cloudy  skies 
prevail,  and  hence  there  is  almost  always  an  excellent  opportunity  of  studying  the 
clouds.  The  most  frequent  fair  weather  clouds  are  Cumulus,  which  have  flat  bases 
and  rounded  tops,  and  which  are  illustrated  in  the  first  cloud  photograph.  They 
start  to  form  in  the  morning  of  a  bright  day,  grow  larger  and  larger  until  after  the 
warmest  part  of  the  day  is  past,  then  decrease  in  size,  and  disappear  as  a  rule  late 
in  the  afternoon. 

The  highest  of  all  clouds  are  called  Cirrus.  They  are  composed  of  ice  specks 
that  form  in  the  very  cold  atmosphere  6  or  7  miles  above  the  earth's  surface.  They 
always  look  very  thin,  white,  feathery,  and  isolated.  Cirrus  clouds  are  not  good 
"storm  signals"  as  a  rule,  and  they  appear  in  nearly  all  kinds  of  weather.  The 
"tufted"  Cirrus  is  shown  in  the  second  cloud  photograph. 

It  is,  however,  an  excellent  indication  of  a  coming  storm  when  the  sky  becomes 
overcast  wiih  a  very  thin,  whitish  veil  through  which  the  sun  shines  brightly, 
provided  this  whitish  veil  thickens  into  a  greyish  veil  within  an  hour  or  two,  or 
more.  The  sun  will  be  scarcely  visible  through  the  greyish  veil,  and  there  usually 
will  be  ram  or  snow  within  about  6  or  8  hours  after  these  veil-like  clouds  over- 
spread the  sky.  The  greyish  veil  is  a  lower  cloud  than  the  white  veil,  and  between 
the  elevations  at  which  these  two  types  form  there  are  often  to  be  seen  clouds  of 
great  beauty — Mackerel  Sky,  for  instance. 

High,  thin  clouds  nearly  always  move  eastwardly  very  rapidly,  though  they 
seem  to  move  slowly,  just  as  an  airplane  does  when  very  high  in  the  air. 

WHAT  CLOUD  MOVEMENTS  INDICATE. 

One  of  the  chief  benefits  to  be  derived  from  watching  the  lower  clouds  is  by 
observing  the  direction  toward  which  they  travel  They  are  thick,  and  their 
direction  changes  like  the  wind.  If  they  are  moving  from  an  easterly  direction 
they  indicate  stormy  weather  in  Maryland  and  Delaware,  but  if  they  are  advancing 
from  a  westerly  direction  clearing  weather  is  usually  near  at  hand. 

19 


OUR  CLIMATE 


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MARYLAND  AND  DELAWARE 


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OUR  CLIMATE 


The  local  storms  of  Summer,  however,  come  from  a  westerly  direction,  and 
when  thunderheads,  illustrated  in  the  fourth  cloud  photograph,  appear  in  the 
western  sky  on  a  hot,  sultry  day,  they  are  an  excellent  sign  of  approaching  rain. 
Hence,  the  saying — 

"When  clouds  appear  like  hills  and  towers, 
The  earth's  refreshed  by  frequent  showers." 

Rings  around  the  sun  or  moon,  or  halos  and  coronas,  are  rather  poor  indicators 
of  coming  weather  changes,  and  they  chiefly  show  that  between  you  and  the  sun 
or  moon  there  are  thin,  icy  clouds. 

WHAT  THE  BAROMETER  INDICATES. 

If  the  barometer  falls  on  a  hot,  sultry  day,  the  winds  usually  being  south  or 
southeast,  expect  a  thunderstorm  in  the  afternoon. 

If  the  barometer  begins  to  fall  and  the  wind  shifts  from  north  to  northeast 
expect  cloudy  weather,  increasing  northeast  winds,  and  rain  or  snow  within  12 
hours.  If  a  northeast  storm  sets  in  it  will  often  last  from  24  to  36  hours. 

A  slowly  falling  barometer,  with  a  brisk  southwest  wind,  usually  indicates 
clearing  weather,  although  it  may  also  bring  a  west  or  northwest  blow.  When 
the  barometer  starts  to  rise  rapidly  with  a  southwest  wind,  the  wind  will  quickly 
change  to  west  and  northwest. 

Normal  barometer  is  about  30.00  inches  at  sea-level.  A  "high"  barometer 
in  Summer  is  about  30.25  to  30.50  inches,  and  in  Winter  about  30.50  to  30.75 
inches,  or  higher.  High  barometer  indicates  fair  weather,  unless  the  wind  shifts  to 
noriheast  or  east.  A  "low"  barometer  in  Summer  is  about  29.75  to  29.50  inches, 
and  in  Winter  about  29.50  to  29.25  inches,  or  lower.  Unsettled  weather  will 
usually  continue  as  long  as  the  barometer  remains  low. 

HOW  TO  LOCATE  THE  STORM'S  CENTER. 

The  first  thing  that  a  weather  forecaster  wishes  to  know  is  where  a  storm's 
center  is  located.  By  "storm  center"  we  mean  the  center  of  a  low  pressure  area 
that  chiefly  controls  the  weather  at  any  particular  time.  The  winds  usually  give  us 
this  information  with  some  degree  of  accuracy,  when  a  weather  map  can  not  be 
consulted.  This  is  the  rule :  Face  the  wind,  and  the  center  of  the  low  pressure 
area  will  he  off  to  one's  right. 

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MARYLAND  AND  DELAWARE 


OUR  CLIMATE 


For  instance,  in  Maryland  and  Delaware :  A  southerly  wind  usually  means 
that  a  storm's  center  is  off  to  the  westward,  and  that  temperature  above  normal  will 
continue.  A  southwest  wind  usually  means  that  a  storm's  center  is  passing  east- 
wardly  over  the  Lake  Region,  and  that  sunshiny  weather  is  in  prospect.  A 
northeast  wind  usually  means  that  the  barometer  has  risen  considerably  on  or  near 
the  North  Atlantic  Coast,  and  it  may  also  mean  that  a  storm  area  is  coming  up  the 
Atlantic  Coast,  from  the  Southwest ;  this  is  the  condition  most  favorable  for  stormy 
weather.  A  north  wind  usually  means  that  we  are  passing  out  from  under  the 
influence  of  a  storm  area  that  has  reached  the  North  Atlantic  Coast,  and  that  fine 
weather  will  prevail.  Light,  variable  winds  usually  mean  that  there  will  be  little 
change  in  prevailing  weather. 

The  most  important  winds  in  Maryland  and  Delaware  are  northeast,  south, 
southwest,  and  northwest.  The  other  winds  are  usually  of  short  duration. 

An  unfavorable  weather  sign  is  a  backing  wind — that  is,  a  wind  that  passes 
from  south  to  northwest,  through  the  southeast,  east,  northeast,  and  north ;  this  is 
the  long  and  stormy  way  round.  A  shifting  wind,  on  the  other  hand,  is  always  a 
good  sign — that  is,  a  wind  that  passes  from  south  to  northwest  through  the  southwest 
and  west;  this  is  the  short  way  round,  and  usually  means  a  quick  clearing 
up. — James  H.  Spencer,  in  the  Baltimore  Sunday  Sun. 


MARYLAND  AND  DELAWARE 


22 


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25 


OUR  CLIMATE 


HOW  STORM  TRACTS  AFFECT  THE  WEATHER  IN 
MARYLAND. 

The  winds  move  in  great  whirls  that  travel  in  endless  procession  across  the 
United  States  from  the  Pacific  to  the  Atlantic.  They  may  be  likened  to  eddies  in 
a  river  that  are  carried  downstream  by  the  current.  These  "wind  whirls,"  which 
occur  only  in  the  lower  region  of  the  atmosphere,  are  carried  across  the  country  by 
contact  with  the  swift  upper  currents  of  air  that  are  ever  moving  eastwardly  across 
the  United  States. 

The  winds  that  bring  us  the  stormy  weather  whirl  spirally  inward,  as  shown 
in  diagram  No.  1 .  These  whirls,  commonly  called  Lows,  may  be  1 ,000  miles  or 
more  in  diameter,  but  they  vary  greatly  in  size  and  shape.  They  reach  the  Pacific 
Coast  from  the  North  Pacific  Ocean,  and  we  locate  them  first  on  the  weather 
map  in  Oregon,  Washington,  or  farther  north.  They  travel  across  the  United  States 


CANADA 


MEDICIME 
HAT 


DENVER 


MEMPHIS 


Diagram  No.  1 — A  low-pressure  whirl,  or  storm  area,  moving  across  the  United  States  by 
the  northern  route  Note  that  the  winds  blow  spirally  inward  The  broken  arrow  shows  the 
approximate  path  of  the  storm.  Whirls  of  this  character  bring  the  stormy  weather  to  the  regions 
over  which  they  pass  They  often  travel  from  the  North  Pacific  Ocean* to  the  North  Atlantic 
Ocean  within  a  week.  Following  these  whirls  are  the  fair  weather  areas,  with  winds  blowing 
outwardly. 

at  about  the  average  speed  of  an  express  train,  but  the  movement  is  much  faster 
in  Winter  than  in  Summer.  All  the  important  whirls' do  not  come  from  the  Pacific, 
but  the  majority  of  them  do. 

26 


MARYLAND  AND  DELAWARE 


The  Lows,  or  storm  areas,  that  chiefly  affect  the  weather  and  climate  of 
Maryland  move  across  the  country  by  one  of  three  storm  paths  that  are  fairly  well 
denned.  One  path  is  along  the  Canadian  border;  another  is  over  Colorado, 
Kansas,  Missouri,  the  Ohio  Valley,  and  New  England  or  the  St.  Lawrence  Valley  ; 
and  the  third  is  over  Utah,  New  Mexico,  the  Gulf  States,  and  thence  noitheast- 
wardly  near  the  Atlantic  Coast.  These  storm  paths  are  indicated  by  the  arrows 
in  diagram  No.  2. 


THREE  PRINCIPAL  PATHS. 

Thus,  we  find  that  two  of  the  three  principal  storm  paths  across  the  United 
States  pass  to  the  northward  of  Maryland,  and  this,  perhaps,  is  the  chief  reason 
why  this  State  has  a  climate  that  is  characterized  by  an  abundance  of  sunshine,  a 
mild  Winter,  and  an  unusually  long  "growing  season."  Naturally  you  will  ask, 
"What  particular  difference  can  it  make  in  the  weather  and  climate  of  Maryland 
whether  the  center  of  a  storm  area  reaches  the  Atlantic  by  a  path  passing  to  the 
southward  or  to  the  northward  of  Maryland  ?"  The  answer  to  this  question  may 
be  stated  thus: 

If  a  storm  area  passes  to  the  southward  of  Maryland  the  winds  over  this 
section  must  back  through  the  southeast,  east,  northeast,  north,  and  northwest,  and 
that  is  the  long  and  stormy  way  round.  Furthermore,  this  section  will  be  in  the 
colder,  or  northern,  quadrant  of  the  disturbance,  where  the  air  will  be  drawn  down 
from  Canada.  On  the  other  hand,  if  a  storm  area  passes  to  the  northward  of 
Maryland  the  winds  over  this  section  must  shift  through  the  southwest,  west,  and 
northwest,  and  that  means  a  quick  change  to  clearing  weather.  It  is  a  safe  wager 
that  on  any  day  in  Maryland  when  the  wind  is  changing  from  south  to  northwest 
(through  the  southwest  and  west)  we  will  have  partial  or  full  sunshine.  Moreover, 
when  the  disturbance  is  passing  to  the  northward  of  Maryland  this  section  will  be 
in  the  warm,  or  southern,  quadrant,  where  the  air  will  be  drawn  northward  from 
the  Sunny  South. 

It  will  be  noticed  on  diagram  No.  2  that  the  storm  areas  that  travel  the  middle 
route  are  deflected  northeastwardly  after  reaching  the  Lower  Ohio  Valley.  The 
Appalachian  Mountains  are  probably  responsible  for  this  deflection,  although  the 
moist  Lake  Region  may  be  another  factor,  since  the  "fuel"  of  the  storm  area  is 
water  vapor.  The  storm  areas  that  travel  the  southern  route  are  usually  deflected 
northeastwardly  by  high  pressure,  or  heavy  air,  over  the  Atlantic  Ocean  as  they 
approach  the  Atlantic  Coast.  In  other  words,  these  disturbances  always  travel  the 
path  of  least  resistence. 

27 


OUR  CLIMATE 


THE  CAUSE  OF  FAIR  WEATHER 

Areas  with  winds  that  whirl  spirally  outward  also  cross  the  country  with  great 
frequency.  These  are  the  high-pressure  areas,  or  Highs,  that  bring  fair,  cool,  and 
settled  weather  to  Maryland.  A  great  number  of  them  travel  all  the  way  across 
the  country,  with  the  North  Pacific  Coast  as  the  starting  point.  A  considerable 
number  also  drop  down  from  Canada — some  from  the  Medicine  Hat  Region  north 
of  Montana  and  the  Dakotas,  and  others  from  the  Hudson  Bay  Region.  Most 


MEDICINE 


CANADA 


N^^  »^     v^/^— 

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\  DENVER ^    BALTJ^ 


MEXICO  N 


Diagram  No.  2— Most  of  the  storm  areas  that  affect  the  weather  of  Maryland  travel  across 
the  United  States  by  routes  indicated  by  the  arrows  in  this  diagram.  Storm  areas  that  passover 
the  southern  route  cause  the  greater  portion  of  Maryland's  precipitation  in  Fall,  Winter,  and 
Spring,  and  they  are  known  as  "northeasters"  because  the  wind  blows  Irom  the  northeast  while  the 
storm  area  is  approaching  from  the  Southwest  Storm  areas  that  travel  the  two  northern  routes 
cause  only  brief  periods  of  stormy  weather,  or  none  at  all  ;  they  cause  a  shift  in  the  wind  from 
S.  to  NW.,  through  SW.  and  W. 

of  them,  except  those  from  the  Hudson  Bay  Region,  reach  the  Atlantic  Coast  via 
paths  lying  to  the  southward  of  Maryland,  and  as  soon  as  they  settle  over  the  South 
Atlantic  States,  as  most  of  them  do,  the  temperature  begins  to  rise  in  Maryland, 
the  weather  remaining  fair. 

Suppose  that  Nature  had  reversed  the  conditions  under  which  these  areas  of 
low  and  of  high  pressure  reach  the  Atlantic,  most  of  the  Lows  passing  to  the  south 
of  Maryland  and  most  of  the  Highs  passing  to  the  north  of  Maryland.  Under 
such  conditions  there  would  have  been  an  excess  of  north  and  northeast  winds  and 
cold,  stormy  weather  in  this  section,  instead  of  the  pleasant  weather  and  moderate 
temperature  that  are  actually  enjoyed  in  Maryland  most  of  the  time. — James  H. 
Spencer,  in  the  Baltimore  Sunday  Sun. 

28 


CONTENTS 

PAGES 

Barometer,  meaning  of  changes  in 22 

Clouds,  Alto-Cumulus,  photograph '. 23 

Cumulo-Nimbus,  photograph 25 

Cumulus,  photograph 20 

tufted  Cirrus,  photograph 21 

what  they  indicate 19 

Frost,  average  date  of  earliest  killing  in  Autumn,  at  selected  stations 17 

average  date  of  latest  killing  in  Spring,  at  selected  stations 17 

Growing  Season,  length  of,  in  Maryland  and  Delaware  and  at  selected  stations..  12 

Highs,  or  High-Pressure  Areas,  what  they  bring 28 

Humidity,  relative,  average  Summer,  at  selected  stations 18 

Ivow  Pressure  Whirl,  diagram  of 26 

Ivows,  or  L,ow-Pressure  Areas,  what  they  bring 26,  27 

Outstanding  Features 4 

Precipitation,  annual  nutnberof  days  with  .01  inch  or  more,  at  selected  stations..  12 

average  annual,  at  selected  stations 11 

average  annual,  by  States 5 

Maryland  and  Delaware,  annual  and  monthly  6 

Maryland  and  Delaware,  average  annual,  chart 5 

Seasons,  the,  in  Maryland  and  Delaware,  character  of 4 

Snowfall,  average  annual,  at  selected  stations 11 

Storm's  Center,  how  to  locate.. 22 

Storm  Tracks,  how  they  affect  the  weather  in  Maryland 26,  27,  28 

Temperature,  annual  mean,  at  selected  stations 13 

aveiage  annual,  by  States 7 

average  annual    number  of  days  with  maximum  90°  or 

above,  at  selected  stations 13 

average  annual   number  of  days  with   minimum  below 

freezing,  at  selected  stations 16 

average  annual  number  of  days  with  minimum  below 

zero,  at  selected  stations 16 

average  Summer  and  average  Winter,  at  selected  stations 15 

average  Summer,  at  selected  stations 18 

highest  and  lowest  of  record,  at  selected  stations 14 

Maryland  and  Delaware,  average  annual ,  chart 7 

Maryland  and  Delaware,  average  date  of  last  freezing  in 

Spring,  and  average  date  of  first  freezing  in  Autumn,  chart 9 

Maryland  and  Delaware,  average  monthly  and  annual 8 

Tracks  of  Storm  Areas,  chart 28 

Weather  Signs  in  Maryland  and  Delaware 19 

Wind,  prevailing  direction  of,  at  Baltimore 10 

Winds,  changes  in,  and  their  meaning 24 

Winter  Sunshine 4 

29 


LOAN  OEPT 


Photomount 
Pamphlet 

Binder 
Gaylord  Bros. 

Makers 
Syracuse,  N.  Y. 

PAT.  JAN  21,  1903 


oi 


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